I’ve insulated four campervans. The first one grew mould within three months. The second was freezing in winter because I believed the marketing hype about reflective foil. The third was better but still had condensation issues I didn’t fix until I ripped half of it out six months later. The fourth? Finally got it right. This experience led me to understand the importance of Insulation And Soundproofing for Campervans.

That’s £1,400 worth of insulation materials I’ve ripped out and binned because I did it wrong. Another £280 in mould treatment and repainting. And countless nights shivering in Scotland or sweating in Spain because I convinced myself that 10mm of bubble wrap would somehow defy physics.

This guide is everything I wish I’d known before I started. Not the marketing claims. Not the YouTube videos where everything works perfectly. The actual reality of insulating a metal box in the UK, what genuinely works, and how to avoid the expensive mistakes I made.

Why Insulation Actually Matters (More Than You Think)

Before we get into materials and techniques, understand this: insulation and soundproofing for campervans is the single most important decision in your entire conversion. Get it wrong and nothing else matters. Your £800 diesel heater won’t help if all the heat escapes through the roof. Your expensive ventilation system won’t stop condensation if cold metal meets warm air.

I’ve met people who spent £15,000 on beautiful furniture, fancy electrical systems, and Instagram-worthy interiors, then cheaped out on insulation. Every single one regrets it.

What proper insulation does:

• Keeps you warm in winter (obviously)
• Keeps you cool in summer (less obvious but equally important)
• Prevents condensation (the real killer)
• Reduces noise (makes the van liveable)
• Saves fuel (your heater runs less)
• Protects your build (mould destroys furniture and health)

What it costs to get it right:

• Budget option: £250-£400 for a medium wheelbase van
• Decent job: £400-£600
• Premium materials: £600-£900

What it costs to get it wrong:

• Ripping it out and starting again: £300-£600 in new materials
• Mould treatment: £80-£150
• Repainting damaged areas: £60-£120
• Lost time: 2-4 days of work redone
• Health issues from mould: Priceless (and expensive)

I’ve been in both camps. Trust me, spending £500 upfront beats spending £800 fixing it later.

Understanding Heat Transfer (The Boring But Critical Bit)

Skip this if you just want to be told what to buy. But if you want to understand WHY certain materials work and others don’t, this matters.

Heat moves three ways:

1. Conduction — Heat moving through solid materials (metal van walls conducting cold inside)

2. Convection — Heat moving through air currents (cold air sinking, warm air rising)

3. Radiation — Heat moving as infrared energy (like sunlight warming the van roof)

Different insulation materials tackle different types of heat transfer. This is why people get confused.

R-Value explained:

R-value measures thermal resistance. Higher number = better insulation. But thickness matters too.

• Celotex 25mm = R-value of 1.15
• Celotex 50mm = R-value of 2.30
• Sheep’s wool 50mm = R-value of 1.32
• Reflectix 10mm = R-value of 0.15 (basically useless without air gaps)

The key number is thermal conductivity (λ or lambda), measured in W/mK (watts per metre-kelvin):

• Lower = better
• PIR boards (Celotex/Kingspan): 0.022 W/mK (excellent)
• Sheep’s wool: 0.038 W/mK (good)
• XPS foam: 0.034 W/mK (good)
• Bubble foil alone: 0.041 W/mK (poor)

Thermal bridging (the sneaky heat thief):

Metal conducts heat really well. Your van is a metal box with ribs, pillars, and structural elements. These create “thermal bridges” where heat bypasses your insulation entirely.

I didn’t understand this in my first build. I filled every gap with insulation, thinking more = better. But the metal ribs were still conducting cold straight through, creating cold spots and condensation.

The solution: You can’t eliminate thermal bridging completely in a van, but you can minimize it by:

• Breaking contact between metal and interior surfaces
• Leaving air gaps for ventilation
• Using insulation with good thermal resistance
• Accepting some thermal bridging is inevitable

Insulation Materials: What Actually Works

I’ve used pretty much every material available. Here’s the honest truth about each.

Celotex / Kingspan (PIR Rigid Boards)

What it is: Polyisocyanurate foam boards with foil facing on both sides. This is what most professional converters use, and it’s what I use now.

Cost: £4-£8 per square metre depending on thickness and where you buy

Thicknesses available: 25mm, 50mm, 75mm, 100mm (for vans, you’ll mostly use 25mm and 50mm)

Thermal performance:

• λ = 0.022 W/mK (excellent)
• 25mm gives R-value of 1.15
• 50mm gives R-value of 2.30

Pros:

• Best thermal performance for thickness
• Moisture resistant (doesn’t absorb water)
• Rigid — easy to cut and fit between ribs
• Foil facing acts as radiant barrier
• Widely available (Wickes, Screwfix, Travis Perkins)
• Relatively affordable

Cons:

• Can’t compress into curves (you’ll have gaps)
• Not eco-friendly (plastic foam)
• Produces toxic fumes if it burns (though unlikely in a van)
• Needs careful installation to avoid thermal bridging

Where I use it:

• 50mm on the roof (between ribs)
• 25mm on the walls (between ribs)
• 25mm on the floor (under subfloor)

Installation tips:

Cut it 5-10mm oversize for friction fit between ribs. Use expanding foam around edges ONLY — never behind the board (creates thermal bridging). Leave 10-15mm air gap between metal and insulation for ventilation where possible.

Real-world performance:

In my current van with 50mm Celotex on the roof and 25mm on walls:

• Winter night at -2°C outside: 8-10°C inside without heating (about 10°C gain from body heat and residual warmth)
• With diesel heater running: Maintains 18°C using 0.15-0.2L fuel per hour
• Summer day at 28°C outside: 22-24°C inside in shade (4-6°C cooler)

Cost for medium wheelbase van:

• Roof (50mm): £165 (8 sheets at 2400x1200mm)
• Walls (25mm): £95 (6 sheets)
• Floor (25mm): £50 (3 sheets)
• Total: £310

Sheep’s Wool (Thermafleece)

What it is: Actual sheep’s wool, treated against moths and fire-proofed. Eco-friendly option that’s gaining popularity.

Cost: £8-£15 per square metre (more expensive than PIR)

Thermal performance:

• λ = 0.038 W/mK (good but not as good as PIR)
• 50mm gives R-value of 1.32
• 100mm gives R-value of 2.64

Pros:

• Breathable (handles moisture brilliantly — this is huge)
• Eco-friendly and sustainable
• Naturally fire-resistant
• Compresses into awkward spaces
• No need for vapor barriers (wool regulates moisture naturally)
• Feels nice to work with (no itching like fiberglass)
• Excellent sound absorption

When considering a campervan build, remember that Insulation And Soundproofing for Campervans can significantly enhance your comfort and quality of life on the road.

Cons:

• More expensive per square metre
• Takes up more space for equivalent R-value
• Harder to source (not in every builders’ merchant)
• Moths can be an issue if not properly treated
• Heavier than PIR
• Can settle over time in vertical applications

Where it works best:

• Wall cavities where you want breathability
• Areas where you can fit thicker insulation
• Full-time living situations (the breathability matters more)
• Awkward curves and gaps where rigid boards don’t fit

Installation tips:

Wear gloves even though it’s softer than fiberglass. Stuff it in but don’t compress it too much — wool insulates by trapping air. Use around 100mm for walls and roof if you have the space. Secure with mesh or fabric to prevent it falling down.

Real-world performance:

I used wool in van #2 for the walls. Thermal performance was decent but not quite as good as PIR of equivalent thickness. The big win was moisture management — I had far less condensation compared to van #1. But it was more expensive and took up more interior space.

Cost for medium wheelbase van (100mm thickness):

• Full coverage: £450-£650 depending on supplier

My verdict: Brilliant if you’re building for full-time living and can afford the space and cost. For weekend/part-time use, PIR gives better thermal performance per millimetre.

XPS Foam (Extruded Polystyrene)

What it is: Closed-cell foam boards, usually pink or blue. Common in building insulation.

Cost: £4-£7 per square metre

Thermal performance:

• λ = 0.034 W/mK (good)
• 50mm gives R-value of 1.47

Pros:

• Moisture resistant
• Relatively affordable
• Easy to cut and shape
• Lighter than PIR

Cons:

• Not as good as PIR thermally
• Can compress over time
• Less widely available in useful sizes
• Doesn’t have foil facing (need separate vapor barrier)

My experience: I tried this in one section of van #3. It worked fine but wasn’t noticeably better than PIR, and PIR was easier to source in the sizes I needed.

Verdict: Decent option if you can’t get PIR, but PIR is generally better for vans.

Reflectix / Bubble Foil (The Marketing Lie)

What it is: Bubble wrap with foil facing. Marketed as miracle insulation.

Cost: £2-£5 per square metre

Thermal performance:

• λ = 0.041 W/mK when used correctly (poor)
• Without air gaps: R-value of about 0.15 (useless)
• With 25mm air gaps on both sides: R-value of 1.0-1.5 (better but impractical in a van)

The marketing claim: “Reflects 97% of radiant heat!”

The reality: Only works if you have 25mm air gaps on BOTH sides. In a van, you can’t create these air gaps practically. Stuck flat against metal or trapped behind panels, it’s basically expensive bubble wrap.

Pros:

• Very cheap
• Lightweight
• Easy to install
• Works as a vapor barrier
• Good for blocking radiant heat IF you have air gaps

Cons:

• Terrible insulation without air gaps
• Marketing claims are misleading
• People use it as primary insulation and wonder why they’re cold
• Creates condensation issues if used incorrectly

Where it actually works:

Window covers: With an air gap between glass and foil, it reflects heat back out in summer and keeps heat in during winter. This is a good use.

Vapor barrier: Over proper insulation (PIR or wool), it provides a vapor barrier to prevent moisture reaching cold metal. This is how I use it.

NOT as primary insulation. Just don’t. I tried this in van #1 because I believed the marketing. I froze. The maths doesn’t lie.

My verdict: Useful as part of a system (vapor barrier or window covers), useless as primary insulation. Anyone telling you 10mm of bubble foil is adequate insulation for a UK winter is either lying or has never actually used it.

Spray Foam (Professional Application)

What it is: Two-part polyurethane foam sprayed into all cavities by professionals. Expands to fill every gap.

Cost: £800-£2,000 for professional application in a medium wheelbase van

Thermal performance:

• λ = 0.026-0.030 W/mK (excellent)
• Fills every gap perfectly
• No thermal bridging at all

Pros:

• Best possible coverage
• Fills every cavity and awkward gap
• No thermal bridging
• Excellent R-value
• Air-tight seal
• Professional application means it’s done right

Cons:

• Expensive
• Can void van warranty (check with manufacturer)
• Makes van panels impossible to remove later
• Can trap moisture if not done correctly
• Permanent — you can’t easily change your mind
• Needs professional installation (not DIY)

My experience: I’ve never used it personally but I’ve helped a mate whose van was spray foamed. Performance was excellent — genuinely the best-insulated van I’ve been in. But when he needed to access wiring later, it was a nightmare. Had to cut away foam and it made a horrible mess.

My verdict: Only worth it if:

• You have the budget (£1,500+ minimum)
• This is your forever van
• You’re 100% sure of your electrical and plumbing layouts
• You’re not planning to make changes later

For most people doing DIY conversions, PIR boards give you 90% of the performance at 25% of the cost, with the flexibility to change things later.

Closed-Cell Foam Sheets

What it is: Thin closed-cell foam sheets, usually 3-10mm thick. Sometimes used for soundproofing.

Cost: £1-£3 per square metre

Thermal performance: Poor (λ = 0.040 W/mK for 10mm)

Where it’s useful:

• Sound deadening (we’ll cover this later)
• Moisture barrier
• Gap filling

Where it’s not useful:

• Primary insulation (too thin, poor R-value)

Multifoil Insulation (Aluthermo, Actis, SuperQuilt)

What it is: Multiple layers of foil with wadding between them. Marketed as thin but high-performance.

Cost: £6-£12 per square metre

Thermal performance:

• Claimed: R-value of 1.5-2.5 for 20-40mm thickness
• Reality: Only achieves this with air gaps, proper installation, and ideal conditions
• Without air gaps: Similar to bubble foil (poor)

The controversy:

There’s ongoing debate about these products. Independent testing often shows lower performance than manufacturer claims, especially in retrofit applications like vans where you can’t maintain proper air gaps.

My experience: I tried Actis Hybris in van #2 on the advice of someone who swore by it. Thermal performance was disappointing. Maybe I installed it wrong (the instructions are complex), but PIR was simpler and performed better.

My verdict: Too expensive for questionable performance. PIR is cheaper, simpler, and has proven performance that doesn’t rely on perfect installation conditions.

Soundproofing: The Other Half of the Puzzle

Insulation and soundproofing are different. Insulation stops heat transfer. Soundproofing stops noise. Some materials do both. Most don’t.

An uninsulated, unsoundproofed van is a tin can. Every stone hitting the underside sounds like a gunshot. Every raindrop is amplified. Road noise is constant. You can’t have a conversation at motorway speeds.

Soundproofing transforms the experience. It’s the difference between a commercial van and a vehicle you actually want to spend time in.

How Sound Moves

Sound vibrates through solid materials (the metal van body) and travels through air. To stop it, you need:

1. Mass — Heavy materials that vibrations can’t easily move through

2. Damping — Materials that absorb vibration energy and convert it to heat

3. Decoupling — Breaking the connection between vibrating surfaces

4. Absorption — Materials that trap sound waves (like foam or wool)

Soundproofing Materials

Dynamat / Silent Coat / Car Soundproofing Mats

What they are: Butyl rubber sheets with aluminum facing. You stick them to metal panels to dampen vibrations.

Cost:

• Dynamat: £250-£400 for a van (premium brand)
• Silent Coat: £180-£280 (what I use)
• Budget alternatives: £80-£150 (eBay Chinese brands)

How they work: The butyl rubber absorbs vibration energy, preventing panels from resonating and amplifying noise.

Where to apply:

• Floor (entire floor ideally)
• Wheel arches (critical — stones hitting here are loud)
• Roof (at least 50% coverage)
• Door panels
• Behind cab seats

Installation:

1. Clean metal with panel wipe or isopropyl alcohol
2. Warm the adhesive side with heat gun (makes it stick better)
3. Cut to size for each panel
4. Peel backing and apply
5. Roll firmly with a roller to eliminate air bubbles and ensure contact

Critical: This needs to be above 15°C to stick properly. I tried applying Silent Coat in my garage in December. It wouldn’t stick. Had to wait until April.

Coverage recommendations:

You don’t need 100% coverage (despite what manufacturers claim). Focus on the noisiest areas:

• Floor: 70-80% coverage (focus on wheel arches and rear)
• Roof: 50-60% coverage
• Doors: 60% coverage
• Wheel arches: 100% coverage

My coverage:

• Used 9 sheets of Silent Coat (each 4.6kg, 50cm x 80cm)
• Covered about 70% of the floor, 60% of roof, wheel arches completely
• Cost: £225
• Time: 2 full days

Results: Massive difference. Before soundproofing, stones hitting the underside were painfully loud. After, they’re just a dull thump. Road noise reduced significantly. Rain is no longer deafening.

Sound absorption (foam/wool)

After damping the metal panels, you still have airborne noise. This is where sound-absorbing materials help.

Sheep’s wool is excellent for this — it absorbs sound far better than PIR boards. If you’ve used wool insulation, you’re already sorted. If you’ve used PIR, you might want to add some absorption.

Acoustic foam (like studio foam) can be added in cavities, but it’s usually overkill for a van. The insulation and interior lining provide enough absorption for most people.

My Actual Installation Process (What I Do Now)

This is the process I follow after learning from three failed attempts. This is for a medium wheelbase van using PIR boards.

Phase 1: Preparation (1 day)

1. Strip and clean:

• Remove all panels, lining, anything attached to walls/roof/floor
• Wire brush any surface rust
• Treat rust with converter
• Clean all metal with panel wipe
• Let dry completely

2. Mark ribs and fixing points:

• Mark where all ribs, pillars, and structural elements are
• Identify where you’ll need to run cables later
• Take photos for reference

3. Plan your layout:

• Decide where furniture will attach (you’ll need blocking in these areas)
• Identify areas that need service access (don’t fully seal these)

Phase 2: Soundproofing (2 days)

Day 1: Floor and wheel arches

Materials needed:

• 6-8 sheets of Silent Coat or equivalent
• Heat gun
• Roller
• Sharp knife
• Panel wipe

Process:

1. Clean floor thoroughly with panel wipe
2. Warm each sheet with heat gun (makes it pliable)
3. Cut to fit floor sections
4. Peel and stick
5. Roll firmly — this is critical, air bubbles reduce effectiveness
6. Pay special attention to wheel arches (100% coverage here)
7. Overlap sheets by 10-20mm at joins

Wheel arches: These get stone chips constantly. Cover them completely. I use two layers in the most exposed areas.

Day 2: Roof and doors

Same process. Focus on areas where you’ll hear noise most:

• Roof above where you’ll sit/sleep
• Door panels
• Behind cab seats

Don’t bother soundproofing:

• Areas that will be completely covered by furniture
• Inside tiny cavities you can’t reach
• The cab (unless you’re really bothered — it adds weight)

Phase 3: Insulation (3-4 days)

Day 1: Roof

Materials:

• 50mm Celotex (8 sheets for medium wheelbase)
• Expanding foam (5-6 cans of Soudal Gap Filler)
• Sharp knife or saw
• Measuring tape
• Safety glasses (foam in eyes is not fun)

Process:

1. Measure each section between ribs — They’re all slightly different. Don’t assume they’re the same width.
2. Cut PIR boards 5-10mm oversize — You want a friction fit. If it’s too loose, it’ll rattle. Too tight and you’ll compress the ribs (not good).
3. Test fit before foam — Make sure it fits snugly.
4. Apply expanding foam around edges only — NOT behind the board. Foam behind creates thermal bridging. Foam around edges seals gaps and prevents air movement.
5. Press board into place — It should friction fit between ribs.
6. Leave 10-15mm air gap between metal and insulation — This is critical for ventilation. I use small spacers (pieces of plastic or foam) to maintain this gap.

Dealing with curves:

Roof curves toward the edges. PIR doesn’t bend. You’ll have gaps. Options:

• Cut narrower strips that follow the curve
• Use expanding foam to fill gaps (not ideal but works)
• Use wool insulation in these areas (better)

I use option 3 — wool insulation in curved areas, PIR in flat sections.

Day 2: Walls

Same process but with 25mm PIR instead of 50mm.

Additional challenge: Windows. You need to insulate around window frames carefully. Leave expansion space (windows get hot in sun). Seal with flexible sealant, not rigid foam.

Cable routing: Before you insulate, think about where cables will run. I leave channels between insulation and metal for cables. Makes life much easier later.

Day 3: Floor

Floor insulation is non-negotiable. You lose massive amounts of heat through the floor in winter.

Two approaches:

Approach 1 (what I do):

1. 25mm PIR laid directly on metal floor
2. 12mm ply subfloor on top
3. Screw through PIR and ply into original floor (use longer screws)
4. This raises floor by 37mm (annoying but worth it)

Approach 2 (if you can’t lose height):

1. 10-15mm PIR (not ideal but better than nothing)
2. 6mm ply subfloor
3. Raises floor by only 16-21mm

Critical floor consideration: Water and moisture can get under insulation from outside. Use closed-cell insulation (PIR or XPS), never wool. And leave drainage paths for any moisture to escape (small gaps at edges).

Day 4: Vapor barrier and awkward gaps

Vapor barrier: I use Reflectix or basic bubble foil over the PIR insulation as a vapor barrier. This prevents warm, moist interior air from reaching cold metal where it would condense.

Application:

• Staple or tape over insulation
• Overlap joints by 50-100mm
• Tape all seams with aluminum tape
• Don’t stress about perfect coverage — it’s an additional layer, not a critical seal

Fill gaps with expanding foam:

• Around edges of PIR boards
• Where ribs meet roof/walls
• Where pillars create awkward corners

Don’t fill:

• Behind insulation (thermal bridging)
• Ventilation paths (you need air circulation)
• Areas you need to access later

Phase 4: Battening (1 day)

Before you line the walls and ceiling, install battens (timber strips) to attach lining to.

Why battens matter:

1. Create fixing points for lining (you can’t screw through PIR reliably)
2. Create small air gap between insulation and lining (additional thermal break)
3. Hide any uneven insulation

Batten specifications:

• 25mm x 50mm timber (PAR — planed all round)
• Treated timber if possible (moisture resistance)

Where to install:

• Vertically on walls every 400-500mm
• Across roof following ribs
• Around all door and window frames
• Wherever you plan to fix furniture

Fixing battens:

• Use penny washers under screws (spreads load on the insulation)
• Screw through batten, through insulation, into metal ribs
• Check fixing depth — don’t penetrate roof/walls (water ingress)

Cost: £45-£65 for timber for a medium van

Phase 5: Quality Check (½ day)

Before you line over everything, check:

Ventilation paths: Air must be able to circulate. Check you haven’t sealed everything completely. I leave 10-15mm gaps at the top and bottom of walls.

Moisture management: Any water that gets in must be able to get out. Check drainage paths at floor level.

Cable routes: Can you run cables where you need them? Now is the time to install cable conduit or channels.

Thermal bridging: Are there obvious cold bridges you can address? Major ribs can’t be avoided, but check for accidental direct contact between interior surfaces and metal.

Gaps and holes: Fill any gaps that would allow air circulation through the insulation (defeats the purpose).

Common Mistakes (That I Made So You Don’t Have To)

Mistake 1: Using bubble foil as primary insulation

What I did: Van #1, I used 10mm Reflectix everywhere, believing the “reflects 97% of heat” marketing.

Result: Froze in Scotland in October. Condensation everywhere. Black mould on ceiling within 3 months.

Cost: £380 to rip out and redo with proper insulation.

Why it failed: Reflectix needs air gaps to work. I had none. Without air gaps, it’s just thin bubble wrap.

The fix: Ripped it all out. Installed 50mm PIR on roof, 25mm on walls. Problem solved.

Mistake 2: No air gaps for ventilation

What I did: Filled every single cavity completely with insulation. No air gaps anywhere. Proud of myself for thorough coverage.

Result: Condensation behind insulation. Mould on metal panels. Rusting floor around sliding door runners.

Cost: £180 in rust treatment and repainting. Plus the time to partially dismantle and redo.

Why it failed: Moisture needs somewhere to go. Sealed completely, it gets trapped and causes problems.

The fix: Left 10-15mm air gaps between metal and insulation. Added ventilation paths top and bottom of walls. Problem solved.

Mistake 3: Applying soundproofing in cold weather

What I did: Applied Silent Coat in my garage in December. Temperature was about 8°C.

Result: Half the sheets didn’t stick properly. Came loose after a month of driving.

Cost: £80 for replacement sheets.

Why it failed: Adhesive needs warmth to bond properly. Below 15°C, it doesn’t stick well.

The fix: Waited for warmer weather. Used heat gun to warm panels before application. Problem solved.

Mistake 4: Not leaving expansion space around windows

What I did: Insulated tight up against window frames with rigid PIR and expanding foam.

Result: Windows got hot in summer sun, expanded, and cracked one seal. Small leak.

Cost: £95 for professional resealing.

Why it failed: Materials expand and contract with temperature. Rigid foam doesn’t allow movement.

The fix: Left 5-10mm expansion gap around windows. Filled with flexible sealant (Sikaflex), not rigid foam.

Mistake 5: Ignoring thermal bridging

What I did: Filled all cavities but didn’t think about metal ribs conducting cold.

Result: Cold spots on ceiling directly under ribs. Condensation formed here first.

Cost: No direct cost but annoying and inefficient.

Why it failed: Metal ribs conduct cold directly through, bypassing insulation.

The fix: Accepted some thermal bridging is inevitable. Added battens over insulation to create thermal break. Used thicker insulation where possible.

Mistake 6: Using incorrect expanding foam

What I did: Used cheap single-component foam from Pound Shop.

Result: Expanded so much it bowed my roof panels outward. Looked terrible. Also shrunk back after a few months leaving gaps.

Cost: £25 in wasted foam. Time to scrape it out.

Why it failed: Low-quality foam expands unpredictably and doesn’t stay stable.

The fix: Used Soudal Gap Filler (two-component) or Sika Boom (more expensive but excellent). Apply in layers, not huge blobs.

Mistake 7: Forgetting about cable access

What I did: Insulated everywhere, then realized I needed to run cables through insulated areas.

Result: Had to cut channels through insulation, making a mess and reducing effectiveness.

Cost: Time and frustration.

Why it failed: Didn’t think ahead about electrical layout.

The fix: Plan cable routes BEFORE insulating. Leave channels or conduit for cables.

Dealing With Condensation (The Real Enemy)

Condensation is what makes or breaks a van conversion. It’s not dramatic like a leak, but it’s relentless and destructive.

Why condensation happens:

Warm air holds more moisture than cold air. When warm, moist air touches cold metal, it cools rapidly and can’t hold the moisture anymore. The moisture condenses into water droplets.

In a van:

• You breathe out moisture (about 1L per person overnight)
• Cooking generates moisture
• Wet clothes generate moisture
• Even just existing generates moisture

Without proper insulation and ventilation, this moisture condenses on cold surfaces (windows, roof, walls) and causes problems:

• Mould growth
• Rust
• Damp smell
• Damaged furniture and fabrics
• Health issues

The three-part solution:

1. Insulation (prevent cold surfaces)

This is what we’ve been discussing. Proper insulation keeps interior surfaces above dew point, preventing condensation.

My results with proper insulation:

• Winter night at 5°C outside, 18°C inside: Interior roof temperature is 15-16°C
• Windows still condense (single glazing, can’t be avoided)
• Walls and roof stay dry

2. Ventilation (remove moist air)

Essential:

• Roof vent (Fiamma, Maxxair, or Fantastic Fan) — Run on low overnight
• Low-level vents (door vents or similar) — Allow fresh air in

How it works: Fresh air enters low down, warms up, picks up moisture, rises, exits through roof vent. Constant air circulation.

My setup:

• Fiamma Turbo-Vent on roof (runs on low all night, 12V)
• Two low-level vents in rear doors
• Crack a window slightly if I’m cooking

3. Moisture management (reduce moisture)

Practical steps:

• Don’t dry clothes inside (or accept you’ll get condensation)
• Cook with lids on pans (reduces steam)
• Wipe windows in morning (takes 30 seconds)
• Use moisture traps in storage areas (£2-£3 each)
• Air the van during the day when possible

When condensation is still a problem:

Even with all this, you’ll get some condensation on windows (single glazing) and in very humid conditions. This is normal.

Not normal:

• Condensation on walls or ceiling
• Water running down windows in sheets
• Persistent mould growth
• Damp smell that won’t go away

If you have these problems, your insulation or ventilation is inadequate.

Seasonal Performance: What to Actually Expect

I’ve used my current van (properly insulated) for nearly a year. Here’s the reality by season.

Winter (December-February)

Conditions tested:

• Scottish Highlands: -5°C to +2°C
• Lake District: -2°C to +5°C
• Wales: 0°C to +8°C

Inside temperature without heating:

• Overnight: 8-12°C (typically 10-12°C warmer than outside)
• After sleeping (two people): 12-15°C (body heat warms it)

With diesel heater:

• Reaches 18°C from 2°C in about 20 minutes
• Maintains 18°C using 0.15-0.2L fuel per hour
• Stays comfortable overnight on low setting

Condensation:

• Windows: Moderate condensation (expected)
• Walls/ceiling: Dry (no condensation)
• Floor: Stays dry

Morning routine:

• Wipe windows (30 seconds)
• Open roof vent fully for 10 minutes while making coffee
• Done

Verdict: With proper insulation and heating, UK winter is comfortable. Not like a house, but perfectly liveable.

Spring/Autumn (March-May, September-November)

Conditions:

• Temperatures: 8-18°C
• Mix of rain, sun, wind

Inside temperature without heating:

• Stays within 3-5°C of outside temperature
• Warm enough most nights without heating
• Heat rise from cooking usually enough

Condensation:

• Minimal (only if cooking without ventilation)
• Windows get slight condensation overnight if temperature drops suddenly

Verdict: Perfect. Rarely need heating. Rarely too hot. These are the best months for UK vanlife.

Summer (June-August)

Conditions tested:

• Cornwall: 22-28°C
• South England: 24-30°C
• One heatwave in France: 35°C (absolute hell)

Inside temperature:

• In shade: 4-8°C cooler than outside
• In sun: Gets hot (obviously)

Keeping cool:

• Park in shade (critical)
• Open all windows and roof vent (create airflow)
• Reflectix window covers (actually useful here — blocks radiant heat)
• Spend time outside (van is for sleeping and cooking only)

The France heatwave:

• 35°C outside
• Inside peaked at 32°C even in shade with windows open
• Utterly miserable
• We found a stream and stood in it

Verdict: Insulation helps by keeping heat out, but in serious heat (30°C+), nothing short of air conditioning makes a van comfortable. Fortunately, UK doesn’t often hit these temperatures.

Cost Summary: Three Budget Levels

Budget Option (£250-£350)

Soundproofing:

• Skip soundproofing or use budget eBay mats: £0-£80

Insulation:

• 25mm PIR throughout (roof, walls, floor): £180-£240
• Expanding foam: £30
• Vapor barrier (cheap bubble foil): £20

Battening:

• Basic timber: £35

Total: £265-£405

Performance: Acceptable. Better than nothing. Will be cold in serious winter but liveable with good heating.

Standard Option (£450-£650) — What I recommend

Soundproofing:

• Silent Coat or equivalent (70% coverage): £180-£280

Insulation:

• 50mm PIR roof: £165
• 25mm PIR walls: £95
• 25mm PIR floor: £50
• Expanding foam (quality): £42
• Reflectix vapor barrier: £48

Battening:

• Treated timber: £55

Total: £635-£735

Performance: Excellent. Comfortable year-round with appropriate heating/cooling. Minimal condensation with proper ventilation.

Premium Option (£900-£1,200)

Soundproofing:

• Dynamat (80% coverage): £320-£400

Insulation:

• 50mm PIR roof: £165
• 25mm PIR walls: £95
• 50mm PIR floor: £95
• Sheep’s wool for curves and gaps: £85
• Expanding foam (premium): £55
• Reflectix vapor barrier: £48

Battening:

• Premium treated timber: £65

Additional:

• Professional consultation: £150-£200

Total: £1,078-£1,308

Performance: As good as it gets without spray foam. Professional-level results.

Tools You’ll Need

Essential:

• Sharp knife or insulation saw (£8-£25)
• Measuring tape (£5-£12)
• Marker pen (£2)
• Heat gun (for soundproofing) (£15-£45)
• Roller (for soundproofing) (£5-£8)
• Safety glasses (£3-£8)
• Dust mask (£2-£5)
• Work gloves (£4-£10)

Useful:

• Cordless drill (for battening) (£60-£150)
• Panel wipe or isopropyl alcohol (£5-£12)
• Staple gun (for vapor barrier) (£15-£35)
• Aluminum tape (for sealing vapor barrier) (£6-£12)

Total if buying everything: £130-£342 (depending on quality)

My Final Recommendations

After four van builds, here’s what I’d do if I started again tomorrow on a medium wheelbase van:

Day 1-2: Soundproofing

• Silent Coat: 70% coverage focusing on floor, wheel arches, roof
• Cost: £225

Day 3-5: Insulation

• 50mm Celotex on roof
• 25mm Celotex on walls
• 25mm Celotex on floor
• Wool insulation in curves where PIR doesn’t fit
• Expanding foam around all edges
• Reflectix vapor barrier over everything
• Cost: £435

Day 6: Battening

• 25mm x 50mm treated timber battens
• Cost: £55

Total cost: £715 Total time: 6 days working alone

Performance: Excellent thermal insulation, good sound dampening, minimal condensation, comfortable year-round.

This is the sweet spot between cost, performance, and DIY-ability.

Final Thoughts

Insulation isn’t glamorous. Nobody’s instagramming photos of PIR boards. But it’s the foundation of everything else in your conversion.

I’ve been in £30,000 conversions with beautiful interiors that were freezing in winter because they skimped on insulation. I’ve been in tatty old vans with basic furniture that were cosy and comfortable because insulation was done properly.

Spend the money here. Spend the time here. Get it right.

Your future self — shivering in Scotland or melting in Cornwall — will thank you.

And if you cock it up the first time like I did, don’t feel bad. Learn from it, fix it, and move on. That’s what I did.

Now stop reading and go insulate your van. Properly this time.

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Got questions? steve@theferalway.com — I actually respond.